The entire system is set up so as to maximize Messi statistically...that means he completely dominates the play in the final third throughout the season. He's progressively played closer and closer to goal - and it's reached almost to the point where every play needs to run through him or to be run for him if it's going to end up in the back of the net.

They can play without him - they have proven that - forwards like Tello and Pedro simply need to not conceptualize themselves as auxillary to Messi. Which is difficult when the only reason they're in the team consistently - and Villa isn't - is because they're willing to be that.

playing through messi in the final third is a winning formula and has proven to be effective at the highest levels of the game, so why stray from it?

yes, they can win without him but no one fills that center forward role in barca's style better than messi.